This invention relates to a steam flow meter for measuring a flow rate of steam which performs heating or drying in various kinds of apparatuses.
A steam heating apparatus is generally provided with a steam flow meter at the inlet side of the apparatus. The flow meters are based on different principles, however, at any rate, each of them allows the amount of steam consumed to be grasped and, at the same time, allows a proper amount of steam for the material to be heated to be supplied to the apparatus. Furthermore, it is important to correctly understand the property of steam in question to supply a proper amount of steam.
In a conventional manner, for example, a corresponding flow rate is determined by measuring a differential pressure to correspond to the steam flowing through a supply tube, and separately the actual temperature and pressure of the steam in question are measured, and in the end, the flow rate to the correct flow rate of the steam is revised on the basis of the measurements of the temperature and pressure. However, since a conventional flow meter based on the measurement of a differential pressure only has a function of measuring an actual differential pressure, in addition to the flow meter, a thermometer and a pressure gauge are provided to carry out a required revision in the case where a correct amount of steam is determined. This increases the cost of equipment and construction. In order to solve such a problem, JP-A Hei-4(1992)-50620 discloses a flow meter which, in addition to measuring the differential pressure of flow rates in the measuring process, simultaneously measures the static pressure and the temperature to carry out the revision of the temperature and pressure of the flow rate in the measuring Process. This provides an added value to the flow meter per se, and at the same time, dispenses with the separate provision of any measuring means or arithmetic correction unit, thereby allowing the reduction in cost of both the equipment and construction to be planned.
Furthermore, separately providing a means for detection of an amount of material to be heated, such as a flow meter or the like, at the supply side of the material to be heated, and grasping the amount of supply of the material to be heated so as to rationalize the amount of supply, are also widely carried out.
For most of the materials to be heated, by such a rationalization of both the amounts of the supply of steam and the material to be heated, the quantity of heat given from the steam is controlled in a predetermined range with respect to the constant amount of material to be heated, so that the degree of heating of the material to be heated is adjusted.
However, there is a problem in that dust, scales, rust and the like contained within the steam adhere to the heating surface of the steam heating apparatus over time, and therefore, the efficiency of heat transmission to the material to be heated is lowered. A large quantity of heat of the steam exceeding a theoretical quantity is required to carry out a required heating, thus lowering the productivity per unit energy. Moreover, in the case where the lowering of the efficiency of heat transmission can not be correctly grasped, unevenness in heat transmission to the material to be heated occurs, resulting in the lowering of the quality of the products.
Depending upon the kinds of materials to be heated, it is required to maintain a heating temperature which changes little and is highly accurate. For example, food stuffs, medical supplies, chemical articles or the like are deteriorated in quality due to changes in temperature during heating, and therefore, prevention of such deterioration is required.
Accordingly, in the steam heating apparatus in the prior art, measurements of the pressure, temperature and flow rate of steam supplied to the steam heating apparatus, and measurements of the temperatures of the material to be heated before and after heating are carried out in order to precisely detect the lowering of the efficiency of heat transmission. That is, a quantity of heat which can be supplied to the material to be heated is calculated from the pressure, temperature and flow rate of the supplied steam, and then the lowering of the efficiency of heat transmission is detected from a rise in the temperature of the material due to the quantity of the supplied heat.
To that end, even if the flow meter disclosed in the above-described JP-A Hei-4(1992)-50620 is used in order to precisely detect the lowering of the efficiency of heat transmission and to maintain the heating temperature of the material more correctly, the separate provision of a thermometer for measuring temperatures before and after heating of the material to be heated is necessary, and furthermore, operations for performing calculations from their measuring data and adjusting the quantity of supply of the steam or material to be heated are indispensable.
In the prior art described above, since it is necessary to separately provide a measuring unit or arithmetic unit in addition to the steam flow meter, there is a problem in that the total expense for the apparatus using steam is increased, and further, the construction of the apparatus becomes complicated.